The objective of this proposal is to determine the role and mechanisms of kallistatin in repairing vascular injury. Endothelial damage plays a pivotal role in the development of vascular diseases. It has been shown that the number and migratory capacity of endothelial progenitor cells (EPCs) are decreased in patients with cardiovascular diseases. Therefore, restoration of EPC number and function is a promising approach to endothelial repair by providing a continuous source of replenishment for damaged and senescent vessels. Kallistatin, a plasma protein, was discovered in our laboratory. We have demonstrated that kallistatin exerts multiple protective effects against cardiovascular and renal dysfunction by inhibiting inflammation and oxidative stress in animal models and cultured cells. Importantly, kallistatin increases circulating EPC levels and reduces aortic oxidative stress in hypertensive rats, as well as promotes the migration and decreases the senescence of cultured EPCs. Our central hypothesis is that kallistatin prevents vascular damage by stimulating EPC mobilization and functional activity and reducing EPC senescence through decreased oxidative stress and enhanced nitric oxide production. We will pursue the following specific aims: 1) determine the mechanisms by which kallistatin promotes vascular repair by enhancing EPC migration, adhesion, tube formation and proliferation; 2) determine the mechanisms by which kallistatin prevents vascular injury by inhibiting EPC senescence; and 3) determine the novel role of kallistatin in endothelial injury by using kallistatin administration and kallistatin depletion approaches in hypertensive rats, kallistatin transgenic mice and knockout mice. The outcomes of the proposed research are expected to have an important positive impact by providing a novel approach using kallistatin-based therapy to improve endothelial repair for vascular diseases.